1. Field of the Invention
The present invention generally relates to a V/F converter, in particular, to a V/F converter for power inverter.
2. Description of Prior Art
Following the increasing maturity of frequency conversion technology, the application of frequency converter is very popular currently, not only frequently seen in various domestic appliances (e.g., air conditioner, refrigerator, and washing machine), but also applied prevalently in each industrial control.
In frequency conversion application, a V/F converter is usually used, such as: TC9400 series manufactured by MICROCHIP Company and ADVFC32 manufactured by ANALOG DEVICE Company, which are all IC products that convert analogical voltage signal into digital frequency signal, such that the digitization of precision control may be processed conveniently. In said V/F converters, the relationship between input voltage and output frequency is a linear transfer function, which implies a direct proportion relationship between these two values. In all these V/F converters of IC products, an offset adjust pin (e.g., the second leg of TC9400 series and the first leg of ADVFC32) is usually arranged and connected to a variable resistance, the adjustment of which may change the slope of said transfer function during frequency conversion procedure, and thus a more accurate corresponding between the frequency output value and the voltage output value may be obtained.
However, such offsetting adjustment must be handled one by one through artificial manner, which is very uneconomical in a mass production of frequency converter, because it consumes substantial manpower and time. Furthermore, in the mobile structure of a variable resistance, its accuracy and endurance are all inferior to those of a fixed resistance, so the phenomenon of resistance floating is occurred frequently and also influences the accuracy of V/F conversion.
On the other hand, it has been very popular that a microcontroller unit is used in a frequency converter for processing digital control, but the prior frequency converter did not use the microcontroller unit for offsetting the transfer deviation of V/F converter. Therefore, if an existent microcontroller unit is used for automatically offsetting linear deviation of a V/F conversion, not only the cost of manpower and time needed by previously artificial adjustment can be completely saved without additional element cost, but also the unstable problem generated from the usage of variable resistance may be prevented.